This study shows that the use of an LMA instead of an ETT during bronchoscopically controlled PDT significantly improves the visualization of relevant tracheal structures. This was presumed by some observational studies4,9,11 but never before documented in a prospective, randomized study. In our opinion, the improved visibility of tracheal structures should decrease the incidence of such complications that are related to impaired overview inside the trachea. These complications are damage to the rear tracheal wall,12–14 puncture lateral to the midline or above the first tracheal cartilage,15 injury during dilation,6,13,15 ETT cuff rupture4–8,13,14 and loss of airway by accidental extubation4,5,8 with subsequent hypoxia,5,13,14 and puncture of the bronchoscope.16,17
In this study, it was shown that improved visualization with an LMA was achieved because the tip of the bronchoscope could be positioned at the level of the vocal cords. Thus, in contrast to an ETT, the thyroid cartilage was almost always identified easily (Fig. 5). Identification of the prominent thyroid cartilage allowed for reliable and easy definition of the cricoid and tracheal cartilages. Furthermore, unwanted displacement of the bronchoscope was recognized immediately by the disappearance of the thyroid cartilage from the visual field. Besides the probability of decreasing the frequency of some complications, the performance of PDT is clearly facilitated both in patients with anatomical difficulties (short neck and obesity) and in the education of PDT to inexperienced physicians. Furthermore, placing the bronchoscope's tip at the vocal cord level prevented the bronchoscope from being damaged by the puncture needle during PDT.
In 2 patients with the ETT, difficulty identifying the thyroid cartilage required the withdrawal of the ETT until its tip came very close to the level of the vocal cords and resulted in accidental extubation. This complication using an ETT was reported to occur in 1.4% to 3.3% of procedures performed.4,7,8,13 Furthermore, in 1 patient in the ETT group, the bronchoscope was damaged by the puncture needle.
In our opinion, there are further advantages of LMA use. First, optimal position of the LMA could be ensured by a simple medical strip. With the ETT, it is common practice to secure the ETT throughout the entire procedure with the assistance of another person. Second, with the LMA, it was possible to determine the site of tracheal puncture by bronchoscopy alone. With an ETT, additional indirect measures such as palpation of laryngeal structures and transillumination are recommended. This may be difficult in anatomical variations, e.g., in obese patients.
Overall, the rate of complications in this study (Table 3) is comparable with findings in the literature. Many studies and meta-analyses described accidental extubations,4,5,8 episodes of hypoxia,5,13,14 hypercapnia,18–20 and impossibility of LMA introduction.8
During PDT, PaO2 was decreased in both groups. Whereas 3 patients with ETTs showed critically impaired ventilation and hypoxia (PaO2 <60 mm Hg), with an LMA, no case of hypoxia occurred in this study.
In 1 patient, attempts to insert the LMA failed, and PDT was continued after reintubation. Because this happened at the beginning of the procedure, the patient was well oxygenated and neither desaturation nor hypercapnia occurred.
Most studies using an LMA for PDT found minor changes in ventilation or at least a ventilation comparable with an ETT.8,20–24 However, Ambesh et al.7 rated ventilation with an LMA inferior compared with an ETT. This may have been caused by a very high rate of 33% of “potentially disastrous complications” with the use of an LMA (loss of airway, inadequate ventilation of lungs leading to significant hypoxia, gastric distension, and regurgitation) in their study. Experiences in our institutions and by others showed a definitely lower rate of ventilation-associated complications.4,8,9,23,24
Whether using an ETT or LMA, the airway resistance increases by introducing the bronchoscope. Obviously, this results in decreased minute ventilation and consecutive hypercapnia. An increased PaCO2 value as a result of decreased minute ventilation is a well-known problem during PDT, observed with the LMA and with the ETT.18–20 Because the internal diameter of an LMA is larger than an ETT, the increase of resistance will be less pronounced with an LMA than with an ETT (whereas a 5.5-mm bronchoscope reduces the internal cross-sectional area of a 7.5-mm ETT by approximately 44%, the cross-sectional area of an LMA is reduced approximately 17%). Reilly et al.18,19 suggested a relationship between residual cross-sectional area and PaCO2. They found lower PaCO2 values using external ultrasound instead of a bronchoscope for localization of the PDT puncture site. This hypothesis is supported in this study and by other investigations showing lower PaCO2 values during PDT when the LMA was used.8,23 Hypercapnia is of particular importance in neurosurgical patients with decreased intracranial compliance. As cerebral blood flow increases with increased PaCO2, intracranial pressure may increase during PDT in these patients.25
According to the study protocol, tidal volume, respiratory frequency, and PEEP setting at the ventilator remained unchanged, and only excessive leakage volume was minimized by reducing inspiratory pressure. Obviously, in our patients, ventilation was not satisfactory, because PaCO2 increased markedly in both groups. Whereas Dosemeci et al.8 were able to ventilate their patients during PDT via LMA without increased mean PaCO2 (but increase in 38.5% of patients), results of most other studies show increased mean PaCO2 and suggest hypoventilation to be a common problem during PDT.13,18–20
LMA use is frequently rejected because of concerns about the reliability of this type of artificial airway with regard to regurgitation of gastric contents, maintenance of minute ventilation, and PEEP. However, the basis for these concerns has been ameliorated, both in our institutions and by other authors who have investigated the LMA.4,8,9,21,23,24,26 It has been argued that an LMA is not a completely “safe” airway.27,28 However, during PDT, this holds true for an ETT as well. During PDT, the ETT's cuff has to be deflated, and the ETT is situated only 1 or 2 cm inside the trachea, resulting in a partially unsecured airway and decreased minute ventilation. Therefore, we do not consider the LMA to be less secure when compared with an ETT during PDT. Aspiration of gastric contents during PDT29 seems to be a rare complication; it was never observed in our institutions and was not reported in studies and meta-analyses on complications during PDT.4,5,7,13,24,26,30 Nevertheless, the LMA ProSeal™ is recommended for use in patients at risk for aspiration.4,24,26,30
Some intensivists using an LMA did not use the LMA Classic.24,30 Verghese et al. used the intubating laryngeal mask™, as we did in our previous investigation,9,21 mainly because of the facility to reintubate the trachea in case of any emergency.31–34 However, in some cases, the intubating laryngeal mask was situated above the base of the tongue.9 In our trials using the LMA Classic, we did not encounter this problem because the aperture of the LMA could always be placed above the larynx. The ProSeal LMA, which is equipped with an additional drainage lumen, was also used with success.24,30 The assumed advantage regarding the drainage of gastric fluids during PDT is discussed above. However, a disadvantage of the lumen of a ProSeal LMA is that it is comparable with that of an ETT, which may result in greater airway obstruction than with the LMA Classic.
This study has several limitations. The assessment of visibility and quality of ventilation with a semiquantitative score is potentially biased by the knowledge of the airway used. However, a double-blinded assessment is difficult to achieve, because the airway used is inevitably identified during the PDT procedure. To minimize any potential bias, we used strict and clear descriptions of each quality criterion (Appendix 1). Furthermore, the number of patients was too low to prove the effect of improved visualization on the rate of complications. To prove an effect of an LMA on reducing the complication rate from 10% to 5%, a sample size of 159 patients would have been necessary. Also, the assigned patients manifested only minor disturbed pulmonary function with a mean PaO2/FIO2 of approximately 380. In our study, the indication for tracheostomy was mainly related to neurologic disturbances, and PDT was performed early, within the first week. Therefore, it was not possible to document how well this technique might work in patients with severe lung injury requiring higher peak inspiratory pressure or PEEP.
In summary, the LMA technique showed definite advantages regarding visualization of relevant tracheal structures and the dilation process compared with an ETT. Ventilation during PDT was superior with the LMA, and bronchoscope damage and accidental loss of airway occurred in the ETT group only.
Ulf Linstedt, MD, PhD, was involved in planning, study design, conduct, analysis, and manuscript preparation of the study; Michael Zenz, MD, and Andreas W. Prengel, MD, PhD, were involved in study design, analysis, and manuscript preparation of the study; Kirsten Krull, MD, was involved in conduct, analysis, and manuscript preparation of the study; and Dietrich Häger, MD, was involved in conduct of the study.
Special thanks to Mark Huessy, Essex, VT, for his efforts to improve the English style of the manuscript.
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